1. Technical Field
The present invention relates to a piezoelectric material, a piezoelectric member, a piezoelectric element, and a pressure sensor which endure hot environments.
2. Description of the Related Art
Sensors and actuators utilizing piezoelectric elements have been widely used in various applications. It has been expected to use piezoelectric materials which endure hot environments of several hundreds degrees Celsius in such applications as combustion pressure sensors of engines, ultrasonic sensors for continuous monitoring of high-temperature plants in thermal power plants.
Characteristics required for a piezoelectric material which endures hot environments are, for example, that (A) the piezoelectric material should have any phase transition point and any Curie point; (B) the piezoelectric material should have a high melting point; and (C) the piezoelectric material should maintain electric insulation even at a high temperature, etc. Furthermore, it is preferred that (D) resources for raw materials are abundant; (E) conventional techniques for growing crystal can be employed; and (F) large size crystals can easily be produced.
Some piezoelectric materials which can work in hot environments have been reported. Typical examples thereof include (1) quartz (SiO2), (2) gallium phosphate (GaPO4) (for example, see JP 6-326552 A), (3) langasite that contains rare earth elements (La3Ga5SiO14, La3Ta0.5Ga5.5O14, La3Ta0.5Ga5.5-xAlxO14) (for example, see JP 10-54773 A, JP 2005-16984 A, and JP 2010-185852 A), (4) four-component langasite type crystal (Ca3TaGa3Si2O14) (for example, see JP 2010-185852 A), and (5) rare-earth calcium oxoborate (YCa4O(BO3)3).